Alleviation of high temperature stress in strawberry (Fragaria×ananassa, Duch., cv. Nohime) plants infected with arbuscular mycorrhizal (AM) fungi (Gigaspora margarita, Glomus fasciculatum, Gl. mosseae, Gl. sp. R10, Gl. aggregatum) was observed. During the raising seedling in hot season (July and August in 2002), temperatures in both the greenhouse and soil in the pot fluctuated similarly, and the daily maximum temperature reached over 35°C almost every day. Ten weeks after inoculation, incidence and severity of browning in leaves became lower in AM plants than in non-AM (NAM) ones. Root browning occurred in all plots, however, AM plants had lower severity than NAM ones, especially in Gl. mosseae and Gl. aggregatum plots. AM plants gave greater values in the following parameters : no. of leaves and roots, leaf area, diameter of crown and dry weight of leaves and roots than those in NAM ones; Gl. aggregatum plot showed relatively higher dry weight of leaves and roots than the other species. No characteristic relationship occurred between AM fungal infection level or phosphorus content in plants and alleviation of high temperature stress. These findings suggest that high temperature stress was alleviated in AM fungus-infected strawberry plants and the effect differed with fungal species.

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The effects of three environmental factors on the recovery of net photosynthetic rate (Pn) in the senescent primary leaves by the removal of foliage leaves in snap bean plants (Phaseolus vulgaris L.) were examined. Effects of temperature were examined under three different conditions : 23/18, 25/20, and 28/23°C (day/night) . Under these conditions, Pn at 25°C were not affected. Effects of light intensity were examined by covering the primary leaves with 1-3 layers of black cheesecloth. The recovery of Pn on a fresh weight basis decreased with increasing shade level. However, any difference was not observed in Pn on a dry weight basis. Since shading with black cheesecloth increased leaf extension and decreased leaf thickness, the effect of light intensity appeared to be through the effect on leaf morphology. Effects of nitrogen were examined by applying three different levels of nitrogen during the different experimental period. It became evident that the nitrogen level in the nutrient solution applied to plants is an important environmental factor affecting the recovery of Pn.

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Control of water temperature by air flow through a duct connected to the bottom of a hydroponic bed made of microporous film (MP film) was evaluated. Air and vapor can pass through MP film, whereas water cannot do. The relationship between water temperature in the bed and air flow velocity was investigated using small devices (1m×0.05m) . Water temperature decreased immediately after air flow treatment, and a low velocity (1.2-1.5ms^-1) was more effective than other rates (0 m s^-1, 10-11 m s^-1, 20-21 m s^-1) . The temperature under low humidity (RH=31-33.6%) after the air flow treatment was 6.6°C lower than that before treatment. High humidity decreased the effect of the air flow treatment. Spinach grew in a polystyrene bed, a MP film bed and a MP film bed with air flow treatment ; the MP film bed consisted of polystyrene side wall and a MP film bottoms. The average temperature during air flow treatment was 2.8°C lower than that in polystyrene bed, and the maximum difference between the two treatments was 5.0°C during cultivation from July 4 to 10. The decrease in temperature can be controlled by stopping the treatment. These results indicate that a hydroponic bed made of MP film with a ventilation device is useful for controlling the solution temperature.

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To evaluate rosetting characteristics under artificial conditions in growth chambers, seedlings of 13 Eustoma grandif forum (Raf.) Shinn. cultivars were grown in 5 different day/night temperature regimes (14h photoperiod, 100μmol⋅m^-2⋅s^-1 PPFD) . Evaluated bolting rates (EBRs) decreased with temperature and differed among cultivars. Rosette indexes (RIs) in the growth chambers were higher than those in the greenhouse. However, close correlations were found between the RIs in the growth chambers and the greenhouse (r=0.856) . These results indicate that it is also valuable to evaluate rosetting characteristics of Eustoma cultivars under artificial conditions and to classify them based on the RIs obtained there. To examine the effect of daylength on the bolting, seedlings of six Eustoma cultivars were grown under two artificial photoperiodic conditions kept at 30°C day/20°C night (100μmol⋅m^-2⋅s^-1 PPFD) . The photoperiods of short day (SD) and long day (LD) conditions were 12h and 12h+4 h night break (22: 00-2: 00), respectively. LD promoted Eustoma bolting. Both easy- and hardly-bolting cultivars were little affected by the daylength. In the cultivars classified into the intermediate ranks of rosetting, the bolting was stimulated by the night break (LD) .

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We examined changes of mineral composition in leaves of muskmelon (Cucumis melo L.) after removal of fruits at various intervals. Total chlorophyll in first leaf on bearing branch was increased in 30-day and 45-day fruit-removal. In 60-day fruit-removal, it decreased rapidly from 15 days, and reached the lowest level at the time of harvesting. Phosphorus in leaves on bearing branch increased rapidly from 30 days in 45-day and 60-day. Potassium in leaves of main stem were lower in fruiting than in non-fruiting, and there were lower in the treatments with the fruit for longer periods. In first leaf on bearing branch, potassium in leaves of the main stem increased gradually up to 60 days. In fruiting, it increased slightly, but in 60-day, it decreased rapidly from 30 days, and reached about 1/3 of that of non-fruiting 60 days. In all treatments, calcium in first leaf on bearing branch increased rapidly up to 30 days, and then slightly decreased. The decrease rate was highest in 60-day. Magnesium in leaves on bearing branch increased up to 60 days. These results indicated that mineral composition varied with stage of fruiting and position of leaves. Potassium moved into fruits, and most strongly affected first leaf on bearing branch closest to fruits, suggesting development of etiolation. In further studies, it is necessary to examine relationship between mineral composition and quality of the fruit, and to improve quality of the fruit.

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We have hypothesized that seasonal changes of light quality in daylight influence photomorphogenesis of plants. Further, we also have speculated that the patterns of its changes differ from place to place, and this difference has been useful in the formation of a vegetation at each place. In the present study, photon flux (PF) in the spectral regions of 300-400 nm (UV), 400-500 nm (B), 500-600 nm (G), 600-700 nm (R), 700-800 nm (Fr) were simultaneously observed at noon at Sapporo (Aug. 2000-Mar. 2002), Gifu (Jan. 2000-Dec. 2002) and Naha (Jan. 2001-Sep. 2002) in order to determine the differences in the seasonal changes of light quality in daylight for different places. There was a similar trend in the changes in spectral ratio of B, G and R/photosynthetic photon flux (PPF) on fine days among the three cities. The G/PPF ratio was almost constant during the observation, and there was a negative correlation between variations of B and R/PPF ratios. These changing patterns were in agreement with the one in the previous paper (Ishii and Yamazaki, Environ. Control in Biol. (2002) 40: 207-213) . On the other hand, it was found that the daylight in Naha abundantly comprised the spectral region of B. Further, the spectral composition of B in Naha was entirely different from those in the other two cities. In Naha, the ratios of 410-419, 420-429 and 430-439 nm regions to B were high and the ratios of 450-459, 460-469, 470-479, 480-489 and 490-499 nm regions to B were low as compared with Sapporo and Gifu. These results suggest that the seasonal changes in spectral photon flux of daylight in each city are mainly influenced by solar altitude.

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